Energy and Human Evolution
by David Price
Life on Earth is driven by energy. Autotrophs take it from solar radiation and heterotrophs take it from autotrophs. Energy captured slowly by photosynthesis is stored up, and as denser reservoirs of energy have come into being over the course of Earth's history, heterotrophs that could use more energy evolved to exploit them, Homo sapiens is such a heterotroph; indeed, the ability to use energy extrasomatically (outside the body) enables human beings to use far more energy than any other heterotroph that has ever evolved. The control of fire and the exploitation of fossil fuels have made it possible for Homo sapiens to release, in a short time, vast amounts of energy that accumulated long before the species appeared.
By using extrasomatic energy to modify more and more of its environment to suit human needs, the human population effectively expanded its resource base so that for long periods it has exceeded contemporary requirements. This allowed an expansion of population similar to that of species introduced into extremely, propitious new habitats, such as rabbits in Australia or Japanese beetles in the United States. The world's present population of over 5.5 billion is sustained and continues to grow through the use of extrasomatic energy.
But the exhaustion of fossil fuels, which supply three quarters of this energy, is not far off, and no other energy source is abundant and cheap enough to take their place. A collapse of the earth's human population cannot be more than a few years away. If there are survivors, they will not be able to carry on the cultural traditions of civilization, which require abundant, cheap energy. It is unlikely, however, that the species itself can long persist without the energy whose exploitation is so much a part of its modus vivendi.
The human species may be seen as having evolved in the service of entropy, and it cannot be expected to outlast the dense accumulations of energy that have helped define its niche. Human beings like to believe they are in control of their destiny, but when the history of life on Earth is seen in perspective, the evolution of Homo sapiens is merely a transient episode that acts to redress the planet's energy balance.
Ever since Malthus, at least, it has been clear that means of subsistence do not grow as fast as population. No one has ever liked the idea that famine, plague, and war are nature's way of redressing the imbalance -- Malthus himself suggested that the operation of "preventive checks," which serve to reduce the birth rate, might help prolong the interval between such events (1986, vol. 2, p. 10 [1826, vol. 1, p. 7]). 1 And in the two hundred years since Malthus sat down to pen his essay, there has been no worldwide cataclysm. But in the same two centuries world population has grown exponentially while irreplaceable resources were used up. Some kind of adjustment is inevitable.
Today, many people who are concerned about overpopulation and environmental degradation believe that human actions can avert catastrophe. The prevailing view holds that a stable population that does not tax the environment's "carrying capacity" would be sustainable indefinitely, and that this state of equilibrium can be achieved through a combination of birth control, conservation, and reliance on "renewable" resources. Unfortunately, worldwide implementation of a rigorous program of birth control is politically impossible. Conservation is futile as long as population continues to rise. And no resources are truly renewable. 2
The environment, moreover, is under no obligation to carry a constant population of any species for an indefinite period of time. If all of nature were in perfect balance, every species would have a constant population, sustained indefinitely at carrying capacity. But the history of life involves competition among species, with new species evolving and old ones dying out. In this context, one would expect populations to fluctuate, and for species that have been studied, they generally do (ecology texts such as Odum, 1971 and Ricklefs, 1979 give examples).
The notion of balance in nature is an integral part of traditional western cosmology. But science has found no such balance. According to the Second Law of Thermodynamics, energy flows from areas of greater concentration to areas of lesser concentration, and local processes run down. Living organisms may accumulate energy temporarily but in the fullness of time entropy prevails. While the tissue of life that coats the planet Earth has been storing up energy for over three billion years, it cannot do so indefinitely. Sooner or later, energy that accumulates must be released. This is the bioenergetic context in which Homo sapiens evolved, and it accounts for both the wild growth of human population and its imminent collapse.
ENERGY IN EVOLUTION
We are caught up, as organic beings, in the natural process through which the earth accepts energy from the sun and then releases it. There has been life on Earth for at least three and a half billion years, and over this time there has been a clear and constant evolution in the way energy is used. The first living things may have obtained energy from organic molecules that had accumulated in their environment, but photosynthetic autotrophs, able to capture energy from sunlight, soon evolved, making it possible for life to escape this limited niche. The existence of autotrophs made a place for heterotrophs, which use energy that has already been captured by autotrophs.
It is not clear how photosynthesis got started, although it is a combination of two systems that can be found singly in some life forms that still exist. But blue-green algae, which are among the earliest organisms documented in the fossil record, already employed the two-stage process that was eventually handed down to green plants. This is a complex sequence of events that has a simple outcome. Carbon dioxide (of which there was an abundance in the earth's early atmosphere) reacts with water through energy from light, fixing carbon and releasing oxygen, and a portion of the energy remains captive as long as the carbon and the oxygen remain apart. Plants release this energy when and where necessary to conduct their metabolic business (Starr & Taggart, 1987).
As time passed, the sheer bulk of life increased, so that more and more energy was, at any given time, stored in living matter. Additional energy was stored when carbon from once-living matter was buried, in ever-so-tiny increments, under the surface of the earth-in deposits that became coal, petroleum, and natural gas as well as in sedimentary rocks containing calcium and magnesium carbonates derived from shells. Of all the carbon that has played a part in the life process, very little was separated out and held apart in this way, but over the course of millions and millions of years, it has mounted up. More and more carbon wound up under the ground, with a greater and greater amount of oxygen in the earth's atmosphere. This separation of carbon and oxygen from a primeval atmosphere in which carbon dioxide and water were abundant represents a vast accumulation of solar energy from the past.
Life evolves to exploit every possible niche, and as autotrophs developed better ways to capture and store the sun's energy, heterotrophs developed better ways to steal it. Independent locomotion was adaptive in the search for nutrients, although it took a little more energy than being buffeted about by the elements. Cold-blooded fish and amphibians were followed by warm-blooded species, which reap the benefits of remaining active at lower temperatures, while using yet more energy in the process. The development of predation opened access to a supply of high-energy food with a further energy investment in procuring it. Throughout the history of life, as increasingly dense reservoirs of energy became available, species that made use of increasing amounts of energy evolved (see Simpson, 1949, pp. 256-57). This is the natural context of Homo sapiens, the most energy-using species the world has ever known.
THE HUMAN ANIMAL
The extent of human energy use is a consequence of the human capacity for extrasomatic adaptation. This capacity makes it possible for human beings to adjust to a wide variety of novel circumstances without having to wait many generations for evolution to change their bodies. A comparison of somatic and extrasomatic adaptation will show just how remarkable an ability this is: If longer, sharper teeth are adaptive for a predator, animals with teeth that are slightly longer and sharper than those of their fellows will have a slight reproductive advantage, so that genes for longer and sharper teeth will have a slightly greater likelihood of being passed on, and so, over the course of time, the teeth of average members of the population will come to be, little by little, longer and sharper. In contrast, a human hunter can imagine a longer, sharper arrowhead; he can fashion it with nimble hands; and if it is really more efficient than the short, blunt arrowheads that everybody else has been using, his peers will soon adopt the new invention. The chief difference between the two means of adaptation is speed: Humans can adapt, relatively speaking, in a flash.
Extrasomatic adaptation is possible because humans are, in the idiom of the computer age, programmable. Somatic adaptation is like building a hard-wired computer to perform a certain task better than a previous hardwired computer. Extrasomatic adaptation is like writing a new program to perform the task better, without having to build new hardware. The use of language, with its arbitrary relationship between signs and referents, makes possible a wide variety of different software.
Programmability -- the ability to learn -- is not unique with human beings, but they have developed the capacity much further than any other species. Programmability probably developed as an evolutionary response to pressure for flexibility. The ability to make use of a variety of different resources runs deep in the human background, for placental mammals arose from ancestral forms in the order Insectivora that presumably ate insects, seeds, buds, eggs, and other animals. When our hominid ancestors came down from the trees to exploit the African savannas, flexibility was again advantageous. Homo habilis and his fellows were furtive little scavengers who picked what they could from carcasses that leopards left behind and rounded out their diet with fruits and nuts and roots (see Binford, 1981; Brain, 1981). They lived by their wits, and natural selection favored hardware that would permit quick-wittedness.
Programmability -- and the consequent capacity for extrasomatic adaptation -- have made it possible for human beings to advance a very old evolutionary trend at a vastly increased rate. Humans are the most recent in the series of heterotrophs that use increasing amounts of energy, but they differ from other species in this lineup in their ability to use more energy without further speciation. Over the course of humanity's short history, greater and greater amounts of energy have been used by the same biological species (see White, 1949, chapter 13).
EXTRASOMATIC ENERGY
Some human innovations have dealt with the fate of energy channeled through metabolic processes. The development of weapons, for example, made it possible to focus somatic energy so as to obtain high-energy foods with much greater efficiency. Man became a hunter. This may have been the innovation that let Homo erectus prosper and permitted his species to radiate out of the African cradle, pursuing game throughout the tropics of the Old World (Binford, 1981, p. 296). Similarly, the use of clothes brought about a conservation of bodily energy that helped make possible the conquest of more temperate regions.
But the most remarkable human innovation is the use of extrasomatic energy, wherein energy is made to accomplish human ends outside the bodies of its users. And the most important source of extrasomatic energy, by far, is fire. Fire was used by Homo erectus in northern China more than 400,000 years ago, and there is sketchy evidence suggesting that it may have been used long before that (Gowlett, 1984, pp. 181-82). Through the use of fire, meat did not have to be rent by main strength; it could be cooked until tender. Fire could be used to hollow out a log or harden the point of a stick. Fire could drive game from cover and smoke out bees. Fire could hold fierce animals at bay.
The exploitation of animal power played an important role in the densification of population that was at the root of what we call civilization. Animals pulled the plow, animals carried produce to market, and animals provided a protein-rich complement to a diet of grain. Wind power was soon utilized to carry cargo by water. But fire remained the most important source of extrasomatic energy, and it made possible the development of ceramics and metallurgy.
Until quite recently, however, there was no real innovation in the fuel used to make fire. For hundreds of thousands of years, fire was made with the tissues of recently deceased organisms-principally wood. The development of charcoal improved on the energy density of untreated wood, and made a substantial contribution to metallurgy. Then, just a few millennia later, the same oxygen-deprived roasting process was applied to coal. In England, coal had been used to heat living space since the Norman Conquest, but the development of coke and its suitability for steelmaking set off the Industrial Revolution. Within an evolutionary wink, petroleum and natural gas were also being exploited, and Homo sapiens had begun to dissipate the rich deposits of organic energy that had been accumulating since the beginning of life. If the slow accretion of these deposits in the face of universal entropy can be likened to the buildup of water behind a dam, then with the appearance of a species capable of dissipating that energy, the dam burst.
ENERGY AND RESOURCES
According to the American Heritage Dictionary, resources are "An available supply that can be drawn upon when needed" and "Means that can be used to advantage." In other words, resources include all the things found in nature that people use-not just the things people use for survival, but things they use for any purpose whatever. This is a very broad concept, as required by the nature of the defining animal. The resources used by other animals consist primarily of food, plus a few other materials such as those used for nest building. But for Homo sapiens, almost everything "can be used to advantage."
For something to be a resource, it must be concentrated or organized in a particular way, and separate, or separable, from its matrix. Ore from an iron mine is a resource in a way that garden soil is not-even though both do contain iron. Similarly, wood from the trunk of an oak tree is a resource in a way that wood from its twigs is not.
Usinga resource means dispersing it. When we quarry limestone and send it off to build public monuments, or when we mine coal and burn it to drive turbines, we are making use of a concentrated resource, and dispersing it. A large, continuous mass of limestone winds up as a number of discrete blocks spread around in different locations; and coal, after briefly giving off heat and light, becomes a small amount of ash and a large amount of gas. Resources may be temporarily accumulated in a stockpile, but their actual use always results in dispersal.
Resources may be used for their material properties or for the energy they contain. Bauxite is a material resource, while coal is an energy resource. Some resources may be used either way; wood, for example, may be used as a construction material or burned in a wood stove, and petroleum may be used to make plastics or to power cars.
The exploitation of all resources requires an investment in energy; it takes energy to knap flint or drill for oil. The exploitation of energy resources must entail a good return on investment; unless the energy they release is considerably more than the energy used to make them release it, they are not worth exploiting.
Since nothing is a resource unless it can be used, resources are defined by the technology that makes it possible to exploit them. Since exploiting a resource always requires energy, the evolution of technology has meant the application of energy to a growing array of substances so that they can be "used to advantage." In the brief time since humans began living in cities, they have used more and more energy to exploit more and more resources.
THE POPULATION EXPLOSION
The cost of energy limited the growth of technology until fossil fuels came into use, a little less than three hundred years ago. Fossil fuels contain so much energy that they provide a remarkable return on investment even when used inefficiently. When coal is burned to drive dynamos, for example, only 35% of its energy ultimately becomes electricity (Ross & Steinmeyer, 1990, p. 89). Nevertheless, an amount of electricity equal to the energy used by a person who works all day, burning up 1,000 calories worth of food, can be bought for less than ten cents (Loftness, 1984, p. 2). 3